In general, textile printing involves substrates with much higher surface roughness, and much higher absorption of liquid inks than paper. Textile printing techniques known in the art for printing onto clothing, other textile materials, and other objects include silk screening, digitally produced sublimation transfers, and mechanically bonded thermal transfers. Of these methods, it is not economical to produce customized products with silk screening printing. Digitally produced sublimation transfer printing is limited to synthetic fibers or pre-treated nature fibers. Finally, direct digital textile printing requires special expensive printing devices to pretreat and post treat the fabric.
Images printed onto garments and other textiles may be permanently bonded or crosslinked to a final substrate to obtain high adhesive strength, and crosslinked within the images to obtain high cohesive strength. Both means of crosslinking are required to provide excellent resistance to chemical processes, such as cleaners or laundry products, and deterioration from normal use. Pure cohesive strength, which mechanically bonds the image to the substrate through internal crosslinking within the printed image, does not permanently bond colorants to textile fibers. Thermal transfers, wherein the ink mechanically bonds to the substrate, are described in Hare, U.S. Pat. No. 4,773,953. The surface bonded image has a substantial ‘hand,’ with a raised, plastic-like feel to the touch, and relatively poor dimensional stability. In addition, the non-imaged area of the transfer sheet used with the process is transferred to the substrate, without chemical bonding or cross-linking processes (Hatada, U.S. Pat. No. 6,103,042, Koerner, et al. U.S. Pat. No. 5,978,077, de Beeck, et al. U.S. Pat. No. 5,985,503, Clemens, U.S. Pat. No. 4,066,802, Mammino, U.S. Pat. No. 4,064,285, Taniguchi, U.S. Pat. No. 5,981,077, Tada, et al. U.S. Pat. No. 6,017,636, DE-A 27,27,223, EP-A 466,503, JP-A 63296982, WO 90/13063). Olsen, et al. U.S. Pat. No. 5,785,790, Olsen, et al. U.S. Pat. No. 5,679,198, and Olsen, et al. U.S. Pat. No. 5,612,119 disclose a screen-printed support sheet, which may have an embedded layer of microspheres, printed with one or more layers of two-component colors based on polyester resin and an isocyanate hardener. The microspheres may have a reflective layer to allow the transferred image printed thereon to reflect light. If more than one color layer is printed onto the microspheres, then a two-component extender or glue that contains a polyester is covered on top of each color layer. On top of the extender layer or single-color layer is applied a powder of polyester or polyamide elastomer, which is then fused into the color layer. Instead of screen printing, a color copier using a two-component toner may be used for applying the color coatings. The color coatings are subsequently covered with this elastomeric powder, which is then fused into the layer prior to transfer.
Conventional heat-melt thermal printing uses primarily non-active wax or wax-like materials such as hydrocarbon wax, carnauba wax, ester wax, paraffin wax, hot-melt resin, thermoplastic, or polymeric materials, as a heat-melt material. The resulting image has poor permanency since the conventional wax materials are not chemically bonded or otherwise permanently grafted to the substrate, but are temporarily and loosely bound to the final substrate by the melting of wax materials during the transfer process. The resulting image is not durable, with the wax materials being washed away during laundering of textile substrates on which the image is transferred, along with the dyes or colorants that form the image in the thermal ink layer.
The natural tendency of cotton fibers to absorb inks causes an image printed on a cotton substrate to lose resolution and become distorted. Liquid inks, other than sublimation inks, wick or are absorbed by cotton or other absorbent substrates, resulting in printed designs of inferior visual quality, since the printed colors are not properly registered on the substrate. This is especially true when aqueous based ink paste is used for coating and fixing purposes as disclosed in Reiff, et al., U.S. Pat. No. 5,607,482.
Cooper, et al. in U.S. Pat. No. 4,216,283, teach a xerographic process of dry image transfer by means of adhesive toner materials. The electrostatic image is developed with a low melting temperature dry toner composition containing a thermoplastic agent to yield an image that is pressure-transferred to a receptor surface. This process uses both low melting temperature plasticizer and foamable microspheres to treat toner material in order to achieve the adhesiveness between toner and substrate. However, it does not chemically bind the toner to the final substrate, and thus, the image has poor permanency qualities.
Natural fiber substrates must be pretreated to permanently accept sublimation dyestuffs and resist chemical processes, such as cleaners or laundry products, and deterioration from normal use. Pretreatment is performed in the early stage of textile printing, and the pretreated fibers may not be suitable for designs applied at a later stage, which greatly limits commercial applicability. DeVries et al., U.S. Pat. No. 4,021,591 disclose that substrates may be surface treated to improve the quality of images received on cotton or other absorbent substrates. Polymer surface coating allows the ink layer to bond to the substrate, and reduces the absorbency of the ink by the substrate thereby improving the image quality. However, grossly coating the substrate results in excess margins which extend beyond the image, and which can be seen with the naked eye, and which add hand to the fabric. The excess coating reduces the aesthetic quality of the printed image on the substrate. Furthermore, the coating tends yellow with age, which is undesirable on white and other light colored substrates. Yellowing is accelerated with laundering, exposure to heat, chemicals, sunlight, or other harsh conditions.
Hale, et al., U.S. Pat. No. 5,431,501, reduce the hand by printing a surface preparation material over the entire image on an intermediate substrate, but not beyond the boundaries of the image. The image is then transferred from the medium to the final substrate by applying heat and pressure, so that the surface preparation material permanently grafts the ink solids to the substrate.
In electrophotographic recording processes, a “latent charge image” is produced on a photoconductor. This image is developed by applying an electrostatically charged toner, which is then transferred to substrates such as paper, textiles, foils or plastic. The image is fixed by the application of pressure, radiation, or heat, or the effects of solvents. (L. B. Schein, “Electrophotography and Development Physics”; Springer Series in Electrophysics 14; Springer-Verlag, 1988).
Hale, et al., U.S. Pat. No. 5,555,813 and Hale, et al., 5,590,600 describe a process of producing images electrostatically using sublimation toner. The images are printed onto a paper substrate, and are subsequently heat transferred onto a substrate comprising polyester at about 400° F. In sublimation transfer printing, solid dyes change to a gas at about 400° F., and have a high affinity for polyester at the activation temperature. Once the gasification bonding takes place, the ink is printed with substantial permanency, and is highly resistant to fading caused by environmental exposure, such as to light, or exposure to certain common chemical processes, such as cleaners or laundry products. However, these applications yield excellent results only when a synthetic material substrate is used, since these dyes have a limited affinity for other materials, such as natural fabrics like cotton and wool.
Conventional electrographic toners typically comprise a polymeric binder resin, a colorant, charge control additives, surface additives, waxes, and optionally, a magnetic material. The binder resins are chosen to be highly chargeable, and bind an image to a substrate at an appropriate softening point (approx. 100.degree. C.). The resins must not contaminate the photoreceptor, while allowing easy cleaning of the photoreceptor. Qualities of the resins are that they are non hygroscopic, disperse the colorant, provide good shelf stability, and are readily processed by a pulverizer. The glass transition temperature is usually between 50° C. to 70° C. If the glass transition temperature is lower than 40° C., the toner shelf life is reduced. Alternatively, if the glass transition temperature exceeds 80° C., the fixing temperature rises, and the process qualities of the toner particles is reduced. Further, if the softening point is less than about 100° C., the toner readily adheres to the printer components, such as the developer or the doctor blades in nonmagnetic, monocomponent developing devices, and the toner susceptible to flocculation and the like, leading to reduced shelf life. The Tg of the polymeric resin is chosen to balance fixing qualities with toner free flow stability and shelf life. Radiation curing or photoinitiating, such as UV-curing, is known in conventional printing and coating arts. These cross-linking reactions occur at a low temperatures and cure rapidly on a heat sensitive substrate. Often, in conventional printing and coatings, a UV-curing system comprises photoinitiators, UV-curable oligomers, and optional dilutes (UV-curable or non-UV-curable). These systems are usually liquids, or they have such a low glass transition temperature, that they are not useful in electrographic or electrostatic printing methods. Conventional UV printing compounds and coatings often generate hard and brittle glossy coatings, due to high cross-linking density, which are not desirable properties in textile printing. Typical UV-curable coatings utilize less energy and significantly less curing time at lower temperature than do thermal curable coatings. Biller, et al., U.S. Pat. No. 5,789,039 describe radiation-curable powder coatings for heat sensitive substrates. The coating composition described therein comprises a cationically catalyzed epoxy resin, a vinyl ether type photopolymerizable resin, a solid plasticizer and a photoinitiator that can generate cationic species. The cross-linked epoxy novolac resins therein have higher stiffness and result in poor “hand” on textile fabrics.
The use of heat by electrographic devices such as laser printers and photocopiers presents the problem of printing heat activated dyes, as recognized in Hale, U.S. Pat. Nos. 5,246,518, 5,248,363 and 5,302,223, when these dyes are to be printed in a non-activated form. Laser printers and photocopiers commonly use relatively high temperature fuser devices to thermally fuse or bind the ink to the substrate, since these devices anticipate that the image will be permanently bonded to the substrate which is printed by the device, and do not anticipate the desirability of subsequent thermal transfer of the image from the printed substrate.
The use of an energy-activated toner on untreated textile substrate is disclosed in Wagner et al., U.S. application Ser. No. 09/978,190. A permanent image is obtained on a textile substrate by printing an energy-activated toner. The energy-activated toner provides high adhesive strength between a final substrate and the toner, and high cohesive strength within toner. To achieve the adhesive bond, the energy-activated toner comprises reactive materials that form covalent bonds with a final substrate, upon activation by the application of energy. The energy-activated toner comprises components having lower molten viscosity that are able to penetrate into an absorbent final substrate, such as natural fiber substrates. Covalent bonding within the image layer that has penetrated into the substrate provides cohesive strength and binds the image to the substrate. To prevent premature crosslinking reaction during printing, the reactive components or groups in the toner are blocked with blocking agents. Heat is used to activate the toner, and covalent bonds are formed between the toner and a final substrate, or between the components of the toner. The energy level needed to bond the toner to final substrates, such as natural fiber substrates, is high, which may cause problems with heat sensitive substrates that tend to yellow or scorch when exposed to relatively high levels of heat energy.
Radiation-curable toners in the form of microcapsulated toner particles may provide resistance to image quality depreciation. A hard polymer shell encapsulates radiation-curable ingredients, which may be liquid. For example, Inaishi, U.S. Pat. No. 5,470,683, describes microcapsule photosensitive toners, whose hard shell breaks after fixing. A curable compound in the core is polymerized by low energy visible light. UV curing technology is also used with transfer toners. Hyde, U.S. Pat. No. 5,565,246, and Held, U.S. Pat. No. 5,275,918, disclose non-electroscopic thermography printing.
Meutter, et al., U.S. Pat. No. 5,905,012, disclose the use of radiation-curable toner to produce high gloss toner images that are resistant to depreciation from external physical influences. Solid materials are suggested therein for use in the UV-curable toner. Meutter et al, U.S. Pat. No. 5,888,689, describe a method producing a cross-linked fixed toner image by using reactive groups that are present in a toner, and reactive groups that are present in a substrate. The glass transition temperature of the resin is above 35° C.
Takama, U.S. Pat. No. 5,822,671 discloses printing a resin-formed image onto a recording medium, such as cloth, followed by treating the recording medium with a plasticizer solution in order to improve the “hand” of the image. The plasticizer penetrates between the resin molecules, thereby imparting pliability to the fabric.
Thompson, U.S. Pat. No. 6,143,454, discloses a dye sublimation toner having high molecular weight, cross-linked polymer resins that neither melt nor become tacky at temperatures needed to sublimate disperse dyes. It is reported that the toner itself does not transfer, while the disperse or sublimation dyes transfer from the intermediate sheet to the final polyester substrate, theoretically reducing the hand. However, a high molecular weight cross-linked resin may not fuse sufficiently to the intermediate sheet, since the resin does not necessarily melt at a fuser roller temperature that is lower than the sublimation temperature.
These techniques suffer various drawbacks, such as requiring specially coated substrates, producing images that suffer from excessive “hand”, relatively low resolution, relatively low imaging speed, poor image quality, vibrancy, and/or permanency when the image is transferred to a fibrous natural material such as cotton or wool. Accordingly there remains a need for a digital printing process using inks or toners, and methods for making same, that provides, for example, satisfactory electrostatic and physical properties of the toners during the printing of an image to an intermediate substrate before permanently affixing the image onto a fibrous natural or synthetic substrate with good quality, vibrancy, permanency and little ‘hand’.